GB2245331A

GB2245331A - Incorporating cables in pipe bundles

Info

Publication number: GB2245331A
Application number: GB9112693A
Authority: GB
Inventors: Kerel Karal
Original assignee: Norwegian Contractors AS
Current assignee: Norwegian Contractors AS
Priority date: 1990-06-14
Filing date: 1991-06-13
Publication date: 1992-01-02
Anticipated expiration: 2011-06-13
Also published as: GB9112693D0; NO902665D0; NO174171C; GB2245331B; NO902665L; NO174171B

Abstract

An underwater pipe bundle 1 comprises at least one pipe (5) to permit continuous lengths of control cables and/or monitoring lines to be fed into the pipe bundle 1. The cables may be in a pipe (6) which itself is pulled through the pipe (5) e.g. by a towing line (8) with the possible aid of a plug (9). Water may be present in the pipe (5) to facilitate the introduction of the pipe (6). <IMAGE>

Description

METHOD AND MEANS FOR ASSEMBLING/DISASSEMBLING CONTINUOUS PIPE LINES ARRANGED IN BUNDLES The present invention relates to long pipe bundles (several kilometers) which are assembled ashore are towed out for installation on a sea bottom.

More particularly, the present invention relates to equipment to and assembling/disassembling of continuous pipe lines and the like, which form part of a pipe bundle.

With "pipe bundle" is in this connection meant a number of pipes inside or assembled together inside a protectional support pipe or casing.

Long pipe bundles for transporting hydrocarbons along the sea bottom are usually assembled ashore on a suitable site by welding together short pipe lengths successively until the desirable total length has been achieved. The ready made pipe bundles are thereafter pulled out in the sea and are being towed to the installation site. If however, the pipe bundle shall include control- and monitoring cables and lines etc. in order to control, supervise and monitor oil/gas production, it is a requirement that such cables and lines shall be delivered and used in continuous lengths. This requirement stipulates special demands to the assembly and characteristics of the pipe bundle.

A known method is to use built-in assemblies. The cables etc. are stretched out on the mounting site, whereafter the protectional pipe for the pipe bundle is realised by pulling pipe lengths over and along the successively fabricated part of the internal pipe bundle together with continuous lengths of control cables and monitoring lines, whereafter the protectional pipe is welded together.

This method requires a large and very long building site. The length of the protectional pipe must be successively pulled over the remaining pipes and cables in the pipe bundle, and the continuous control cables and monitoring lines, in average constituting about 1/4 of the total length of the ready made pipe bundle, which may be several kilometers. The method is not efficient, it is costly and it involves a large risk for damages.

A further known method is "throughpulling". By this method, the entire pipe bundle except for cables etc., is completed, suitably with a parallel assembly of internal parts and the protectional pipe in order to avoid slip-covering as in the above described method. Thereafter, the control cables, monitoring lines, etc. by means of f.inst. railings/rollers, are being pulled into the protection pipe and are sealed off at the ends, such that they constitute part of the internal part of the pipe bundle, in other words, are exposed to the same internal pressure in the protection pipe as in the remaining parts.

A drawback with this method is that there will be a limitation in regard the length which can be pulled into the protection pipe without implying that the force used results in damages on the cables/lines, and further a substantial risk that they get stuck during the pulling operation.

The described method will further result in sealing problems.

In accordance with the present invention, the described problems are solved in that an initial step is established at least one separate pulling pipe in the pipe bundle during the assembly and joint welding of the various element constituting the pipe bundle. The pulling pipe is designed with the aim to include the required control cables, monitoring lines etc., and are being passed through the end walls of the pipe bundle, simultaneously as the remaining space in the pipe bundle remains completely tight. The pulling pipe may further, if desired, be attached to the outside of the protection pipe.

After assembly, the pipe bundle is being launched out in the sea, and since the pulling pipe or pipes are open at the ends, the same will be filled with water. If desired, the pulling pipe may be filled with a liquid which has the desired density and/or friction reducing properties.

Further, continuous lengths of control cables, monitoring lines etc. may be prefabricated so that they are as an added unit confined in a pipe, hereinafter denoted as a guide pipe, and which is made such that it has neutral buoyancy or so little buoyancy or submerged weight as practically possible.

Subsequent to that the pipe bundle is ready mounted, the guide pipe is drawn in and through the pulling pipe by means of a rather small force due to the negligible contact pressure which exists between the cable and the pipe surface. (A result of buoyancy/small submerged weight).

The through-pulling can be carried out, either by a pulling cable built into the pulling pipe, and/or by creating a pressure difference on the fore and rear side of a pulling piston, respectively, on the front end of the guide pipe, which pressure difference is created either by imposing a larger pressure on the rear side of the piston, or providing a subpressure on the fore side of the piston, relative to the hydrostatic pressure on the assembling site inside the pulling pipe.

The material which is utilised in the pulling pipe and the guide pipe, is selected such that the contact friction between wetted surfaces of these materials is as small as possible.

If it is desirable to pull the guide pipe prior to launching of the pipe bundle, this can be carried out in that the pulling pipe firstly is being filled with a friction reducing and buoyancy providing liquid (water, oil) prior to that the work in connection with the pulling operation is initiated.

The internal diameter of the pulling pipe is such selected that the contact pressure during the pulling, due to the guide pipe including control cables, monitoring lines etc. due to stiffness having a wave-shaped run or course and/or by a possible deviation from a straight line which the pipe bundle will attain during the pulling operation, is as little as possible.

The guide pipe may, at any time, also in installed position, be pulled out at one end or the other of the pipe bundle for repairs, inspection or replacement.

The invention shall in the following be further described in connection with some embodiments of the invention, with reference to the accompanying drawings, where: Fig. 1 shows a cross-sectional view of a pipe bundle wherein the pulling pipe forms an integral part of the inside of the pipe bundle.

Fig. 2 is a view showing the pulling pipe mounted on the outside of the pipe bundle.

Fig. 3 illustrates a method used for pulling a guide pipe subsequent to launching of the pipe bundle.

Fig. 4 is illustrating a method used for pulling a guide pipe prior to launching of the pipe bundle.

Fig. 1 is showing a pipe bundle 1 having an external protection pipe 2 forming a protective casing around the ballast pipe 15, production pipe 3, oscillary pipe 4 and to pulling pipes 5 each of which is incompassing a guide pipe 6.

The ballast pipes, production pipes, oscillary pipes and the pulling pipes are all kept in correct position and confined into moulded blocks 13 made for instance of polyethylene and being kept tightly together by means of nylon straps 14, and furthermore being encased by the external protection pipe 2.

The pipe bundle with the hitherto mentioned parts are assembled in known fashion by welding pipe lengths together, and suitable lengths of the polyethylene blocks are successively built around the internal pipes.

The guide pipes 6 circumscribes the controlled cables and monitoring lines. It is a definite requirement that these cables and lines shall be made and presented in full length, and joints are not permitted. Therefore, these parts are prefabricated in a length corresponding to the total length of the pipe bundle and are built into the circumscribing guide pipe 6 prior to being pulled into the pipe bundle by the pulling pipes.

The guide pipes including the control cables and the monitoring lines may with advantage be made with a supplementary length beyond the length of the pipe bundle in order to facilitate coupling at the ends without the need of transition pieces or the like. It may for instance be desirable to pass the cables and lines without transitions directly up to the working platform on a platform rig.

The control cables and the monitoring lines are provided with necessary buoyancy properties by applying these with an external layer of PVC foam or the like.

A further embodiment with an alternative positioning of the guide pipes are shown in Fig. 2, where the pulling pipes 5 are attached with straps 7 to the outside of the protection pipe 2.

Subsequent to launching the pulling pipe will be filled with water, and the pulling operation takes place in that the guide pipe 6 are drawn through the pulling pipe by means of a cable 8 attached to a pulling head 11 on the guide pipe 6 such as shown in Fig. 3.

Fig. 4 is illustrating a preferred method for pulling a guide pipe 6 in the case where the pulling operation can be carried out prior to launching of the pipe bundle. A cable 8, which on beforehand is positioned through the pulling pipe 5 is attached to a plug 9 provided as a liquid sealing 10 against the inside wall of the pulling pipe. The other end of the plug is attached to the pulling head 11 on the guide pipe by means of a cable 12. The liquid sealing 10 of the plug makes it possible to build up a pressure difference on either side of the plug in order to support the progress. The guide pipe slides in liquid 14 inside the pulling pipe 5. The liquid contributes to lower refriction and facilitate the pulling operation.

Claims

Patent claims

1. A long pipe bundle adapted for installation on a sea bottom, which bundle is provided by assembling the required number of sections and parts ashore, and which bundle further shall include control cables and/or monitoring lines in continuous lengths, c h a r a c t e r i z e d i n that the pipe bundle comprises at least one pulling pipe (5) for pulling in and pulling out, respectively, of continuous lengths of control cables and/or monitoring lines.

2. A long pipe bundle in accordance with claim 1, c h a r a c t e r i z e d i n that the unabrupted lengths of control cables and monitoring lines are provided with an external, buoyancy rendering layer.

3. A long pipe bundle in accordance with claim 2, c h a r a c t e r i z e d i n that said control cables and/or monitoring lines are prefabricated as an assembly inside a circumscribing control pipe (6).

4. A long pipe bundle in accordance with claim 1-3, c h a r a c t e r i z e d i n that the inside surfaces of the pulling pipes (5) and the outside surfaces of the guide pipes (6), respectively, have friction reducing properties with water as a lubricant.

5. A long pipe bundles in accordance with claim 1-4, c h a r a c t e r i z e d i n that said pulling pipe (5) is mounted inside the protection pipe (2) of the pipe bundle.

6. A long pipe bundles in accordance with claim 1-4, c h a r a c t e r i z e d i n that said pulling pipe (5) is pressure-tight attached to the outmost protection pipe (2) of the pipe bundle.

7. Method for pulling long continuous lengths of guide cables and/or monitoring lines in a pipe bundle (1) which shall be installed on the sea bottom, c h a r a c t e r i z e d i n that said continuous control cables and/or monitoring lines are being pulled through the ready made pipe bundle inside a pulling pipe (5).

8. Method in accordance with preceding claim 7, c h a r a c t e r i z e d i n that the continuous and unabrupted control cables and/or monitoring lines, which are prefabricated such that they are circumscribed by a guide pipe (6) is being pulled through the pulling pipe (5) as a unit.

9. Method in accordance with claims 7 and 8, c h a r a c t e r i z e d i n that during the making of the pipe bundle (l), pulling cables (8) are positioned in the pulling pipe (5) for pulling said controll cables and/or monitoring lines, or by a guide pipe (6) which circumscribes the controll cables and/or monitoring lines.

10. Method in accordance with claim 7-9, c h a r a c t e r i z e d i n that in order to reduce friction between the pulling pipe (5) and the guide pipe (6) during the pulling in and the pulling out of the operation is utilized friction reducing and buoyancy providing liquids.